1. Field of the Invention
The present invention relates generally to magnetoresistive elements for use in magnetic heads and, more particularly, to a magnetoresistive element utilizing the spin valve effect.
2. Description of the Related Art
FIG. 3 is an illustration of a conventional magnetoresistive element 21 of a spin-valve type. The magnetoresistive element 21 includes a laminate 30 formed on an underlayer 29 composed of a nonmagnetic material such as tantalum, the laminate 30 comprising: an antiferromagnetic layer 22 composed of a PtMn alloy and the like; a first ferromagnetic layer 23 composed of a CoFe alloy and the like; a nonmagnetic conductive layer 24 composed of Cu and the like; and a second ferromagnetic layer 25 composed of an FeNi alloy and the like, deposited on the underlayer 29 in that order. A protective layer 31 composed of a nonmagnetic material such as tantalum is deposited on the laminate 30, and a bias layer 32 comprising a third ferromagnetic layer 26 composed of an FeNi alloy and the like and an antiferromagnetic layer 27 composed of a PtMn alloy and the like deposited in that order is disposed on each of two ends of the laminate 30. An electrode layer 28 composed of Au and the like is deposited on each bias layer 32.
The magnetization direction of the first ferromagnetic layer 23 is pinned in the Y direction in the drawing, i.e., the direction into the plane of the drawing of FIG. 3, as a result of exchange coupling occurring at the interface between the first ferromagnetic layer 23 and the antiferromagnetic layer 22.
The magnetization direction of the third ferromagnetic layer 26 is pinned in the X direction in the drawing as a result of exchange coupling occurring at the interface between the third ferromagnetic layer 26 and the antiferromagnetic layer 27. The magnetization direction of the second ferromagnetic layer 25 is oriented in the direction substantially perpendicular to the magnetization direction of the first ferromagnetic layer 23, i.e., in the X direction in the drawing, as a result of ferromagnetic coupling (magnetic coupling) between the third ferromagnetic layer 26 and the second ferromagnetic layer 25. In other words, a bias magnetic field is applied to the second ferromagnetic layer 25 from the third ferromagnetic layer 26 constituting the bias layer 32.
The magnetoresistive element 21 having the above structure is applied to, for example, a magnetic head incorporated in a magnetic disk device. While supplying a sense current to the first ferromagnetic layer 23, the nonmagnetic conductive layer 24, and the second ferromagnetic layer 25 from the electrode layer 28 via the bias layer 32, a track width region indicated by Tw is positioned to a desired track on a magnetic disk rotating in the Z direction in the drawing. When a leakage magnetic field from the desired track is applied as an external magnetic field in the Y direction in the drawing, the magnetization direction of the second ferromagnetic layer 25 shifts from the X direction in the drawing toward the Y direction in the drawing.
Such a change in the magnetization direction of the second ferromagnetic layer 25 in relation to the magnetization direction of the first ferromagnetic layer 23 causes the electrical resistance in the magnetoresistive element 21 to change. The leakage magnetic field from the desired track is then detected as the change in voltage resulting from the change in resistance. Thus, the magnetoresistive element 21 can read the information recorded on the desired track.
In the conventional magnetoresistive element 21 described above, the magnetization direction of the third ferromagnetic layer 26 pinned in the X direction in the drawing as a result of magnetic coupling with the antiferromagnetic layer 27 may be changed due to a leakage magnetic field from the track adjacent to the desired track on the magnetic disk. Such change in the magnetization direction of the third ferromagnetic layer 26 adversely affects detection characteristics of the leakage magnetic field from the desired track, resulting in inability to accurately read the information recorded on the desired track.
Such disadvantages can be overcome by reducing the thickness of the third ferromagnetic layer 26 and increasing the strength of the magnetic coupling between the third ferromagnetic layer 26 and the antiferromagnetic layer 27. However, in such a case, a sufficient bias magnetic field can no longer be applied to the second ferromagnetic layer 25 due to the decrease in the leakage magnetic field from the third ferromagnetic layer 26, and the magnetization direction of the second ferromagnetic layer 25 cannot be aligned in the X direction in the drawing.
Another possible structure is, as has been known in the art, to replace the bias layer 32 with a permanent magnetic layer 33 made of a CoPt alloy and the like and to apply a leakage magnetic field from the permanent magnetic layer 33 to the second ferromagnetic layer 25 as a bias magnetic field for orienting the magnetization direction of the second ferromagnetic layer 25 in the X direction in the drawing. In this structure, however, the magnetization direction of the portion of the second ferromagnetic layer 25 in contact with the permanent magnetic layer 33 is inhibited from changing freely, resulting in degradation in the detection characteristics of the leakage magnetic field from the desired track.